1. Field of the Invention
The present invention relates to a lower body construction of a vehicle.
2. Description of Related Art
Side sills, which make up part of a monocoque body structure of a vehicle, are provided on both sides of a lower part of a body of the vehicle in such a manner as to extend in a longitudinal direction of the body, and a pillar forming a side framework of a passenger compartment is connected to each side sill. In addition, a reinforcement member is joined to the side sill in the interior thereof in order to suppress the deformation of the side sill towards the interior of the passenger compartment which is caused by an impact load generated when the vehicle is involved in a side collision (refer, for example, to Japanese Patent Publication No. 3315915 (claim 1, FIG. 1)(hereinafter referred as Patent Document No. 1)).
In the lower reinforcement construction of the body of the vehicle described in Patent Document No. 1, since three reinforcement panels (primary, secondary and tertiary reinforcement panels) are provided within a side sill of a box-shaped cross section which is made up of an outer panel and an inner panel and, in particular, the primary reinforcement panel positioned at a middle portion is formed into a shape having a substantially C-shaped cross section, the rigidity of the side sill can be increased.
Even when a reinforcement construction such as one described in Patent Document No. 1 is provided, however, in case a crash energy at the time of a side impact is excessive, a falling deformation (a bending deformation) of the pillar connected to the upper portion of the side sill towards the interior of the passenger compartment is generated, and at an initial stage of the side impact, a twisting deformation of the side sill in which a side of the side sill is made to face obliquely upwards is generated as the side sill is pulled along with the falling deformation of the pillar.
Due to this, at a middle stage of the side impact, since a projecting portion of the primary reinforcement panel which lies on a front side thereof to bear impact is made to face obliquely upwards together with the side sill, the rigidity of the side sill against the impact load is reduced.